The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A254569 The number of unordered pairs (f,g) of functions from {1..n} to itself such that fg=gf (i.e., f(g(i))=g(f(i)) for all i). 1
 1, 7, 84, 1540, 37345, 1145376, 42402871, 1849021504, 93217426857, 5363120671120, 348669188664511, 25418305492373520, 2064813985107357445, 185896884170249831320, 18459391640792004885375, 2012607682674617326564096, 239898601216105901349115537, 31132586664410794285693925664, 4380971763246528510240944123071, 665896706682993760478978112600400 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA a(n) = (A181162(n) - n^n)/2 + n^n. EXAMPLE The a(2) = 7 pairs of maps [2] -> [2] are: 01: [ 1 1 ] [ 1 1 ] 02: [ 1 1 ] [ 1 2 ] 03: [ 1 2 ] [ 1 2 ] 04: [ 1 2 ] [ 2 1 ] 05: [ 1 2 ] [ 2 2 ] 06: [ 2 1 ] [ 2 1 ] 07: [ 2 2 ] [ 2 2 ] CROSSREFS Cf. A181162 (ordered pairs), A254570 (unordered pairs, f and g distinct). Sequence in context: A034323 A172455 A258174 * A183177 A058795 A027459 Adjacent sequences: A254566 A254567 A254568 * A254570 A254571 A254572 KEYWORD nonn AUTHOR Joerg Arndt, Feb 01 2015 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified January 26 16:14 EST 2023. Contains 359833 sequences. (Running on oeis4.)